This invention concerns sulfonated lignin derivative dispersants and, more particularly, the use of such dispersants in thermosol dyeing formulations and processes.
As used herein, the term "lignin" has its normal connotation, and refers to the substance which is typically recovered from alkali paper pulping black liquors, such as are produced in the Kraft, soda and other well-known alkali pulping operations. The term "sulfonated lignin", as used in this specification, refers to the product which is obtained by the introduction of sulfonic acid groups into the lignin molecule, as may be accomplished by reaction of the lignin with sulfite or bisulfite compounds. As used herein, the term "lignosulfonate" refers to the reaction product of lignin which is inherently obtained during the sulfite pulping of wood, and is a principal constituent of the spent sulfite liquor which is derived from that process. Finally, the phrase "sulfonated lignin material" encompasses not only the lignin and lignosulfonate reaction products hereinabove described, but also spent sulfite liquors, which materials may be further reacted (such as for desugaring), purified, fractionated, or the like, as may be appropriate for the particular material involved, and as will be more fully discussed hereinbelow.
It is well known that sulfonated lignin materials may be utilized to considerable advantage as dispersing agents for numerous products, such as clays, insecticides, pesticides, dyestuffs, etc. The provision, however, of a satisfactory dyestuff dispersant represents a particularly difficult task, in view of the fact that it must exhibit a desirable balance of properties, some of which are generally found to be inconsistent with others. Accordingly, it is usually necessary to compromise, and to accept a relatively poor level of performance in one or more respects, in order to achieve good performance levels in other respects. In a disperse or vat dye dispersant, for example, the ideal dispersing agent would exhibit excellent heat stability, coupled with low azo dye reducing and staining properties. It should also minimize foaming, afford maximum milling efficiency (i.e., produce small particle sizes in minimum periods of time), and it should furthermore reduce the viscosity of the dye paste in which it is ultimately employed. Heat stability is especially important in dispersants employed in compositions used in thermosol dyeing processes, so as to ensure effectiveness under the high temperature conditions of fixation.
As an example of the fundamental inconsistency of certain of the foregoing objectives, which has heretofore been fully appreciated, sulfonated lignin products exhibit excellent high temperature stability, but also tend to stain and to produce high levels of azo dye reduction. Conversely, the lignosulfonates exhibit relatively low levels of azo dye reduction, but are deficient from the standpoint of adequate heat stability, for many applications. In general, it has been found that milling efficiency and heat stability are inconsistent properties, and that a dispersant which exhibits one of them will generally tend to be rather deficient, insofar as the other is concerned. Finally, while the lignosulfonate products generally have a somewhat reduced tendency to stain fabrics to which they are applied, as compared to the sulfonated lignin products, the demand remains for lignin-based dispersants that exhibit low levels of staining, particularly in thermosoling applications.
In view of the fact that most disperse and vat dyes are either quinone of azo dyes, the need to avoid reduction reactions is particularly important, since the failure to do so results in the need to utilize unduly large amounts of the dye to compensate for the reduction caused by the dispersant. Many attempts have been made in the art to improve the azo dye reducing and staining properties of sulfonated lignin dispersants, which attempts have generally taken the route of blocking the free phenolic hydroxyl groups of the lignin. Exemplary of such attempts are those described in U.S. Pat. Nos. 3,672,817, 3,763,139, 3,769,272, and 3,865,803. While the foregoing methods are somewhat effective, they tend to be rather costly to carry out, and the results achieved are still less than satisfactory.
Similarly, in view of the need to provide good high temperature or heat stability, so as to enable the utilization of the dyestuff in current conventional dyeing procedures, attempts have been made to improve that property in lignosulfonate products. Typical of such attempts is that which is set forth in U.S. Pat. No. 3,864,276, which describes a dispersant obtained by crosslinking spent sulfite liquor solids and Kraft liquor solids. Ultrafiltration, which may be followed by desulfonation of the product, has also been attempted in order to improve heat stability, and several products made in accordance with such techniques are commercially available. Oxidation and desulfonation of spent sulfite liquor, in an alkaline medium with air or oxygen (as in vanillin production), is yet another approach which has been utilized in an effort to improve heat stability of lignosulfonate products. However, all of the foregoing methods invariably darken the lignosulfonate, thereby elevating the level of staining which is produced when they are utilized; such treatments also tend to increase the azo dye reducing propensity of the product. These results, moreover, are accompanied by less than satisfactory improvement in the high temperature stability characteristics of the products involved. Accordingly, it is the primary object of the present invention to provide novel dispersants produced from sulfonated lignin materials.
It is a more specific object of the invention to provide such dispersants which exhibit an optimal balance of properties, rendering them highly suited for use as dispersants for disperse and vat dyestuffs.
Another specific object of the invention is to provide sulfonated lignin product dispersants which exhibit relatively low staining and azo dye reducing properties, and to provide lignosulfonate dispersants exhibiting greatly improved levels of heat stability, rendering them particularly well-suited for use in thermosol dyeing processes.
Yet another object of the invention is to provide dispersants from sulfonated lignin materials, which afford superior milling efficiency, as compared to similar dispersants of the prior art.
Still another object of the invention is to provide novel dispersants of the foregoing sort, which are relatively inexpensive and simple to produce.
Additional objects of the invention include the provision of dyestuff compositions, pastes, and dye baths based upon dispersants of the foregoing type, and to provide methods for their utilization.